Self-recharging direct conversion electrical energy storage device and method

ABSTRACT

A method and apparatus for collecting and storing the energy emitted by radioisotopes in the form of alpha and or beta particles is described. The present invention incorporates aspects of four different energy conversion and storage technologies, those being: Nuclear alpha and or beta particle capture for direct energy conversion and storage, fuel cells, rechargeable electrochemical storage cells and capacitive electrical energy storage.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 15/728,397 filed Oct. 9, 2017, which is a continuation-in-partof U.S. patent application Ser. No. 13/851,890 filed Mar. 27, 2013, nowU.S. Pat. No. 9,786,399 issued on Oct. 10, 2017, all of which are herebyincorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

The idea of using radioactive materials as direct power sources forapplications requiring long-lived power sources has been investigatedfor many decades. Nuclear power sources for deep space probes have beenused on many NASA programs especially those that last for decades andwhere the probes will not have sufficient sunlight for solar panels tooperate. Nuclear Batteries, also called atomic batteries, have beendeveloped that attempt to exploit the heat or thermal energy of theradioactive materials as well as the alpha and beta particle emissionsenergy through various means. Typically, these devices tend to be largein comparison to typical electrochemical batteries and also tend tosuffer from the emissions of high energy particles including alpha,beta, gamma and neutrons which create human health risks. Besides spaceprobes, small nuclear power sources have been successfully used indevices such as pace makers and remote monitoring equipment.

One area of much research has to do with the direct conversion of betaemissions, i.e. electrons, emitted from radioisotopes that are targetedon a semiconductor material to develop electron-hole pairs and thusgenerate an electrical current in the semiconductor. All of thesedevices suffer from very low efficiencies due to the poor electroncapture cross section of the designs as well as the semiconductormaterial itself. This is the same phenomenon that solar cells continueto suffer from even after decades of work and hundreds of billions ofdollars of investment.

Researchers have recently begun investigating nanotechnologies withwhich to implement nuclear power sources. Some of these include thedevelopment of micromechanical devices that vibrate or rotate inresponse to charge build up within the semiconducting materials.

The underlying reason for pursuing the development of nuclear batteriesis the much wider goal of developing long lasting, low cost powersources. Along these lines, there are many other fields of research thatare producing some interesting and potentially viable power sources. Inparticular, fuel cells and new electrochemical battery technologies lookparticularly promising for small, low cost, high density and long-livedpower sources but none come close to the energy density and longevitythat nuclear power sources offer.

Prior art describes four basic methods of converting radioisotopes intouseable energy sources. Three of these require a double conversionprocess wherein the radioactive sources are used to first generate heat,light or mechanical energy which is then converted into electricalenergy. These multiple conversion processes have extremely lowefficiencies which puts them at a distinct disadvantage to compete withthe fourth method which is referred to as direct conversion.

Of the direct conversion methods, the two that are the most studied arethe semiconductor PN junction conversion and the capacitive chargestorage conversion. The semiconductor conversion processes, also knownas betavoltaics, employs semiconductor technology that suffers fromdevice degradation and very low efficiencies. The capacitive chargestorage devices have problems with large size and very high voltagesthat can reach hundreds of thousands of volts that create materialschallenges that can withstand such high voltages. These problems aremagnified as the devices are scaled down.

A common problem for all of the prior art is that the amount of energythat can be extracted from the radioactive material is a very low leveland at a consistent output which doesn't provide a practical means tosupport real world applications that demand varying amounts of power atdifferent times.

Of the most relevant descriptions of a nuclear batter disclosed in priorart, Baskis, U.S. Pat. No. 5,825,839, describes a direct conversionnuclear battery utilizing separate alpha and beta sources isolated by aninsulating barrier and two charge collector plates, one to collect thenegative beta particles and another plate collect the alpha particles.The two plates become charged and thereby storing the energy in the formof an electric potential the same as a capacitor stores electricalenergy in the form of positive and negative charges on parallel plates.This approach utilizes the balanced alpha/beta charge approach as thepresent invention, but for completely different purposes. In the Baskisdisclosure, a load place across the “battery” allows electrons to flowfrom the negative charged plate to the positively charged plate that issaturated with alpha particles. The recombination of the electrons andthe alpha particles is said to produce helium gas which is vented out ofthe cell. However, this description does not address the recombinationof “free” electrons in the metal plate combining with the alphaparticles producing He gas directly. However, the net effect is thesame, the positive plate will become increasingly positively charged bythe alpha particles producing a stored electric potential across thedevice.

The preferred embodiment of the present invention also suggests the useof balanced alpha and beta charges for greater efficiencies, however,such a requirement is not necessary for it to operate. Additionally, thepresent invention can store the energy of the alpha and or betaparticles in chemical energy form as a chemical battery as well as inelectric potential energy as in a capacitor, as described in alternativeembodiments.

BRIEF SUMMARY OF THE INVENTION

The present invention incorporates aspects of four different energygeneration and storage technologies, those being: Nuclear beta and/oralpha direct conversion, fuel cells, rechargeable electrochemicalstorage cells and capacitive energy storage. In the present invention, aradioisotope, or a mixture of radioisotopes, that emits beta and/oralpha particles is used as the primary energy source while anelectrochemical cell is used as both a secondary energy source as wellas an energy storage mechanism and a capacitor that may be used as aprimary storage device as well.

This disclosure illustrates the core concepts for the construction andmanufacture of the device but by no means limits the actual materials toonly those used as examples and discussed herein nor the embodimentsdescribed. For example, almost any radioisotope can be used as theprimary fuel source for this invention but those that are, at this time,considered safer, more optimal or more readily accessible are moredesirable, especially for devices that could be used for equipment thatwill be in close proximity to humans or animals. As research continuesand future advanced occur, it may become feasible that otherradioisotopes may be well suited for use in this device and thefollowing discussions are by no means intended to limit the invention toonly the specific materials used or discussed herein. This is true forthe materials used including those for the electrochemical andcapacitive storage materials as well.

Additionally, no limitations to the embodiments of the describedinvention are to be inferred. This disclosure is to be interpreted inits broadest sense as to any materials that can be used as well as tothe physical embodiments in which the concepts can be applied. Forinstance, there are hundreds of radioactive materials that can emitalpha and or beta particles and electrochemical batteries and capacitorscan be built in an unlimited number of shapes, sizes, storage capacity,energy densities or materials. There are also many rechargeable batterychemistries that can be used in said present invention and nolimitations as to the type of rechargeable battery or chemistry that canbe used to implement such a device is implied.

Any radioisotopes or combination of radioisotopes that emit alpha and orbeta particles can be used for this device. However, because the devicetakes advantage of both the positive charges of the alpha particle andthe negative charge of the beta particle, to generate dc currentdirectly as well as to provide a charging mechanism for theelectrochemical cell, radioisotopes that produce both particles areexpected to produce greater energy density and efficiencies thanisotopes that produce only alpha or beta particles, however anycombinations of radio isotopes or individual radioisotopes can be used.Radioisotopes that produce low energy alpha and or beta particles areparticularly useful in this application since the emissions can becontained within the structure itself, thus eliminating the healthissues of ionizing gamma and or neutron radiation. Isotopes that producegamma rays and high-energy neutron are less desirable due to theirassociated health risks, and the inability to completely contain theseemissions within the power cell itself. However, the power cell can beadapted for their use for certain applications where these issues arenot a concern, for instance in generating electrical energy from nuclearwaste products stored in long term storage facilities. In this case, thehazardous material is already placed in secured facilities where thehigh-energy emissions cannot harm persons or the environment. Using anyor all available radioisotopes to generate electrical energy would be agood use for this invention. Additionally, space probes could, from ahuman safety standpoint, use any radioisotope material.

While the invention has been described with reference to some preferredembodiments of the invention, it will be understood by those skilled inthe art that various modifications may be made and equivalents may besubstituted for elements thereof without departing from the broaderaspects of the invention. The present examples and embodiments,therefore, are illustrative and should not be limited to such details.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-section of a device according to a preferredembodiment of the invention.

FIG. 2 illustrates a stacked cell configuration.

FIG. 3 illustrates an internal self-recharging process.

FIG. 4 illustrates an attachment and use of an external DC chargecircuit.

FIG. 5 illustrates a discharge process.

FIG. 6 illustrates an embodiment of an implementation in a form of astandard cylindrical battery that is commonly available.

FIG. 7 illustrates a layered approach of placing an amorphoussemiconducting material capable of producing large amounts ofelectron-hole pairs through bombardment of alpha or beta particles.

FIG. 8 illustrates the use of collector plates in or near the amorphoussemiconducting material to aid in the collection of electron-hole pairsbefore they can recombine.

FIG. 9 illustrates the use of a mixture of radioactive material andamorphous semiconducting material in the cell.

FIG. 10 illustrates the cascade of electron-hole pair production withina mixture of the radioactive material and the amorphous semiconductingmaterial.

FIG. 11 illustrates an alternative embodiment of these teachings whereno secondary energy storage is desired.

FIGS. 12a & 12 b illustrate two alternative embodiments of theseteachings where no secondary energy storage desired and where an anionexchange membrane is used with and without a proton exchange orbidirectional ion exchange membrane is used.

FIG. 13 illustrates an alternate embodiment where not ion exchangemembranes are used.

DETAILED DESCRIPTION OF THE INVENTION

For the following discussion, refer to FIG. 1. The device 10, comprisesa rechargeable electrochemical cell 20, such as a Lithium Ion cell,which may be comprised of a cathode plate 19 such as aluminum, a Li ioncapture material 18 such as LiCoO2 (or LiMnO2, or others), anelectrolyte material 17 such as a lithium salt dissolved in organicsolvent with a semipermeable membrane 16 separating the anode andcathode sides of the cell, a carbon anode 14 with an plate 13 such ascopper, a layer of radio isotope material or a mixture of radio isotopematerials 12 which emit alpha and or beta particles, with or without abonding agent (not shown) and a proton exchange membrane layer with anelectrolyte material 11 that is comprised of a highly negatively chargedmaterial, and if necessary, a dielectric insulating layer (not shown).These layers can be rolled up to produce a typical cylindrical batterydevice, referred to in the industry as a “jelly roll,” and shown in FIG.6, or stacked on top of each other in many layers to produce irregularshapes and sizes that would be used in consumer electronic devices asshown in FIG. 2. While the secondary battery technology described hereinhappens to be a Li-Ion type battery, any battery storage technologycompatible with this invention can be used, and a person skilled in theart of battery chemistry and technologies could easily adapt any batterytechnology to be useful in this invention.

For the purpose of the following discussions, where the term membrane isused, it should be understood to mean either just the membrane itself orthe combination of the membrane and the electrolyte material within thecontext of the discussion. Additionally, the membrane and electrolytematerials should be understood to be a membrane material surrounded byan electrolyte material (typically of liquid composition) or asolid-state membrane/electrolyte material that is of a solidcomposition.

The amount of radioisotope material that would be needed in a particularpower cell would depend upon the activity level of the particularmaterial used and the amount of energy that the power cell would need toprovide for a specific application.

FIG. 2 shows a cross section a stacked cell implementation of theinvention as the cells would exist relative to each other. Thisorientation would exist whether individual cells are stacked on top ofeach other or a long single cell was rolled up into a cylindrical shape.In FIG. 6, the layers of the cell would be rolled up upon themselves tocreate a cylindrical form similar in size and shape of commoncommercially available batteries such as “AA”, “AAA”, “C” and “D.” Ofcourse, any shape or size can be constructed by stacking the layersshown in FIG. 2. When stacking layers, the PEM (Proton ExchangeMembrane) layer 11 would be located between the radioisotope materiallayer 12 and the cathode plate 19. Also note that the cathode plate 19and the anode plate 13 are offset with respect to each other and withrespect to the PEM layer 11 so as to prevent shorting the cells whenthey are assembled as well as to allow each cathode plates 19 to beconnected together on one end or side of the cell and the anode plates13 to be connected together on the other end or side of the cell. Thisalso provides a means to connect the anode and cathode to the cellcontacts for external connections.

Theory of Operation

Refer to FIG. 3 for the following discussion. A key aspect to theinvention is the adoption of a proton exchange membrane 11 (PEM) similarto that used in fuel cell technologies. A common type of material usedfor this application is Nafion. There are a number of proton exchangemembranes available that can be used in the present invention. In fuelcells, the PEM is a highly electronegative porous material that allowsthe positive charged “protons” to cross the membrane boundary betweenthe anode and cathode while repelling the disassociated electrons andforcing them to flow around the cell, through an external circuit. ThesePEM characteristics are exploited in the present invention to allow thedoubly positively charged alpha particles 23, which are approximatelythe same size as methanol “protons” to pass through the PEM material 11and collect in the cathode plate 19, while forcing the beta particles22, i.e. electrons, to flow to the anode plate 13 and collect there. Thepositive charges carried by the alpha particles 23 and captured by thecathode plate 19 and the negative charges carried by the beta particles22 and captured by the anode plate 13 will migrate to their respectivecathode 18 and anode 14 regions causing the cell 10 to store thecharges. These charges would then cause the lithium ions 20 to migratefrom the cathode 18 through the electrolyte region 17, across theseparator membrane 16, further across the solid electrolyte interphase(SEI) layer 15, which is formed upon first charging, and finally to insituate themselves, intercalate, within the carbon layers of the anode14, thus completing the charging cycle for a pair of alpha 23 and twobeta 22 particles.

Referring to FIG. 5, when an electrical load is placed across the anodeplate 13 and cathode plate 19, an electric circuit would be completedcausing electrons from the anode 14 to migrate to the anode plate 13,through the external circuit 26 and returning to the cell at the cathodeplate 19. The ideal cell would be achieved when amount of radio isotopicmaterial 12 and the external electrical load 26 were balanced where thetotal electrical current emanating from the radioisotope region into theanode plate 19 and cathode plate 13 were to equal the amount used by theelectrical load 26. This is an ideal condition that is unlikely to everbe achieved. Normally electrical loads have varying power requirementsand this is where the rechargeable electrochemical storage portion 20 ofthe cell 10 plays it role. It will provide additional power to the load26 when it is needed and it will store the excess energy coming from theradio isotope material 12 for later use.

If an electrical load were connected across the anode plate 13 andcathode plate 19, an electric circuit would be completed causingelectrons from the anode 14 to migrate to the anode plate 13, throughthe external circuit 26 and returning to the cell at the cathode plate19. The ideal cell would be achieved when amount of radio isotopicmaterial 12 and the external electrical load 26 were balanced where thetotal electrical current emanating from the radioisotope region into theanode plate 19 and cathode plate 13 were to equal the amount used by theelectrical load 26. This is an ideal condition that is unlikely to everbe achieved. Normally electrical loads have varying power requirementsand this is where the rechargeable electrochemical storage portion 20 ofthe cell 10 plays it role. It will provide additional power to the load26 when it is needed and it will store the excess energy coming from theradio isotope material 12 for later use.

Referring to FIG. 4, as with any secondary electrochemical cell, thepresent invention can be recharged by means of an external chargingcircuit 25 placed across the cathode plate 19 and anode plate 13. Thecharging circuit 25 injects electrons 21 into the anode plate 13 whichmigrate into the anode carbon layer 14 and speed up the lithium ionbattery charging process as shown in FIG. 3.

During discharge, the beta particles 22 (electrons) emitted by the radioisotope layer 12 will flow directly through the anode plate 13 to powerthe external load 26 while the alpha particles will accumulate at theanode, completing the circuit. The current developed from theradioisotope material 12 will power the load reducing the draw from thestored energy of the secondary electrochemical battery cell 20. However,when the current drawn by the load 26 is less than the current developedby the radioisotope material 12, then the excess current will charge thesecondary battery cell 20, thus acting as a charging circuit for thesecondary electrochemical storage battery 20, the same as if thesecondary battery were being charged from an external charging device25.

Because of the affinity of the anode 14 to accept electrons and thehighly electronegative characteristics of the proton exchange membrane(PEM) 11, the beta particles 22 are attracted to the anode plate 13 andcollect there developing an overall negative charge on the plate whichis transferred to the anode carbon layer 14. The increasingly negativelycharged carbon anode 14 attracts positive lithium ions 20 from theelectrolyte 17 causing the migration of the lithium ions 20 from thelithium metal oxide cathode 18. At the same time, the alpha particles 22are attracted by the overall negatively charged proton exchange membrane(PEM) 11 and migrate towards it. The PEM 11 doesn't have any bindingsites for the alpha particle and its physical properties allow the alphaparticles 22 to pass through it to the cathode plate 19 where they areable to bind with the cathode plate 19 and transfer their positivecharges to the cathode plate 19, thereby oxidizing the cathode layer 18and liberating more lithium ions 20 to migrate across the cell to theanode 14.

Alternative Embodiments

Since the radioisotope material 12 continually emits alpha and/or betaparticles 22 and 23, at some point the battery will become fully chargedwith all Lithium ions 20 being intercalated within the carbon materialof the anode 14 but the radioisotope material 12 will still bedeveloping an electrical potential. Some of this unused electricalpotential can be stored in an integral super capacitor (not shown indrawings) surrounding the entire battery device but inside the enclosure31.

During normal operation, helium gas will be produced around the cathodeand PEM or bidirectional membrane materials by the combination of alphaparticles and electrons. This gas is vented off through a vent 36. Sincehelium gas is nontoxic and nonflammable, no special precautions need tobe taken with this emission. However, it could be captured as a usefulbyproduct.

The super capacitor is created by connecting one thin metal plate (notshown in drawings) to the anode plate 13, another thin metal plate (notshown in drawings) attached to the cathode plate 19 and a thininsulating material (not shown in drawings) separating said plates.These two thin metal plates and separator would be wound around theouter surface of the battery as many times as desired to create asuper-capacitor of the desired power characteristics.

Eventually, depending upon the total energy storage capacity of thedevice and the system load demands, one of two conditions will occur.Either the cell will be completely depleted or it will become fullycharged. In the event of a full charge within the electrochemical celland any integral capacitor of the battery, the excess energy will haveto be exhausted as heat. This excess energy is most effectively releasedthrough a resistive material (not shown in drawings) around the outersurface of the cell but inside the protective metal enclosure 31 orincorporated as an integral part of said enclosure 40, so as to radiateoff excess energy as heat into the surrounding environment. A built-incharging and discharging control circuit can be used to control theexcess energy bleed off.

A second situation exists where the device becomes completely dischargedand cannot provide sufficient power for the intended load. At thispoint, the equipment which is powered by the device is turned off or thepower cells are changed out for fresh cells. In either circumstance, theradioisotope will recharge the cell. Current lithium batterytechnologies limit discharge to about 40 percent. A deep discharge willdamage the battery and limit its lifespan. This situation is preventedby a charge control circuit which will prevent battery damage due toovercharging or over discharge.

Alternatively, a standalone self-charging nuclear capacitor is made byapplying a thin layer of the radio isotope to one side of a thin metalfoil then a layer of the PEM or bidirectional membrane material over theradio isotope combined with a binding material followed by the secondmetal foil layer and finally a dielectric membrane is placed on the topof the second foil layer. These layers are then rolled up so that thetwo metal layers are separated by the dielectric membrane. The metalfoil layers are chosen just as in any electrolytic capacitor so that theplates have a propensity to attract and store positive or negativecharges. An example would be aluminum and tantalum foils.

As described above, this capacitor can be implemented directly in thenuclear rechargeable electrochemical power cell by adding the capacitorlayers sandwiched in the radioisotope layer. If the cell designcharacteristics are chosen to incorporate a high voltage capacitor tostore more power, a voltage regulator would be needed to regulate thecharge voltage for the electrochemical cell to protect it from damagefrom over charging and over voltage. A large amount of energy can bestored within this super capacitor that can be used for loads thatdemand very high currents for very short periods of time or if regulatedcan produce lower voltages for longer periods of time, or even othervoltages than that of the battery.

Since alpha particles possess a positive double (+2) charge, they areeasily deflected by electric or magnetic fields. The electric fieldgenerated by the cell construction, with or without the high voltagecapacitor may be effective in driving the alpha particles towards thecathode collector plate and thus, increasing efficiency. Similarly, theaddition of a magnetic material layer that creates a magnetic field thatdirects the alpha particles towards the cathode may also be effective inincreasing efficiency. These same phenomena may also serve to push theelectrons towards the cathode as well.

The amount of radioactivity emissions from materials that are generallyconsidered “safer” than other radioactive materials tend to be too lowpowered for use as a direct energy source for present day electronicdevices. The goal of designing a high energy, long lasting and safenuclear power source is confounded by fundamental material limitationswhere the amount of energy emitted is roughly inversely proportional tothe half-life of the material. That is, the higher the energy output,the shorter the half-life. The goal is to develop devices that can lastmany years to several decades that can also produce the sufficientoutput power to run electronic devices or system without undue risks tohuman life or the environment.

Research into betavoltaics using P-N junctions in silicon and othersemiconductor materials has been focused on creating electron-hole pairsnear the P-N junction of the semiconductor material. These electron-holepairs develop a current across the P-N junction when a beta particle isejected from the radioactive material and travels through thesemiconductor material. Much research has been spent on building 3Dstructures within the semiconductor materials to hold the radioactivematerial in such a manner that would capture as many beta particles aspossible to produce the most electron-hole pairs as the beta particletravels through the semiconductor material. Some research suggests thatas many as 2000 electron-hole pairs can be generated with each betaparticle emitted from a tritium source. There are a couple majorproblems with this approach. The first being that these techniquesrequire expensive silicon wafer production facilities and theirassociated high costs for the base semiconductor wafers. The second isthat the semiconductor materials deteriorate from lattice destructioncaused by the kinetic energy of the beta particles. These devices tendto fail in a relatively short period of time (months to a few years)from even the lowest energy beta emitters. Recent advances insemiconductor P-N junction materials have extended the life of thesedevices to as much as ten years. Destruction of the P-N junction andsemiconductor lattice structure renders the already low efficiencies ofthis method to steadily decrease over time.

Recent research has shown very low-cost amorphous metal oxide materialsto be effective electron-hole generators. Additionally, since amorphousmaterials require neither a fabricated P-N junction layer nor amonocrystalline lattice structure, electron-hole pairs can be generatedfor long periods of time without the concern of the materialexperiencing structure breakdown. A secondary benefit is that thesematerials are very inexpensive.

To increase the electron-hole generation in the present invention, alayer of amorphous semiconducting material, or any other material foundto be generous electron-hole pair generator, can be mixed with orapplied on either or both sides of the radioactive source material thatwill generate a cascade of electron-hole pairs as the alpha and or betaparticles travel through it. See FIG. 7. When a combination ofradioactive material and amorphous semiconductor material is used in theradioisotope layer of the cell as shown in FIGS. 7 through 10, the PEMmaterial must be changed to a bidirectional membrane material. Thebidirectional membrane along with a suitable electrolyte material stillprovides a physical isolation of the radioisotope material 12 & 46 fromthe cathode plate 19 while still allowing alpha particles to flowthrough it to the cathode 19, as was the case with the PEM material, butalso provides a path for electrons to flow from the cathode 19 to fillthe holes in the amorphous semiconducting material that migrate throughthe radioactive/semiconducting material layer and collect at theinterface between this layer and the bidirectional membrane. Since thepresent invention doesn't rely on a fabricated P-N junction layer todevelop a voltage differential across the cell, very inexpensiveamorphous semiconductor material of various kinds can be used as theelectron-hole generation material. The electric field developed by thecell chemistry will naturally draw the electrons towards the anode platewhile the holes will be drawn towards the cathode plate and collect atthe bidirectional membrane layer interface.

Research has also shown that the effective electron-hole generationcapabilities of low energy beta emitters such as tritium extend only afew hundred microns deep into a semiconductor material with mostelectron-hole generation occurring between 1 micron and 10 microns. Twoof the main processes that contribute to the inherent low efficienciesof the semiconductor P-N betavoltaic approach are that there is a highrate of reabsorption of the emissions from the bulk radioactive materialand the recombination of the electron-hole pairs in the semiconductormaterial. The rate of reabsorption is proportional to the thickness ofthe bulk material used in the cell. If the radioactive material isthicker than a few microns to a few hundred microns then the rate ofreabsorption increases with the additional thickness since only thoseemissions closest to the surface of the material are likely to escape tobe used to generate power. On the other hand, semiconductor P-Njunctions that are deposited on the surface of a semiconducting chipstructure are unable to capture many of the electron-hole pairsgenerated at deeper layers of the semiconductor because theelectron-hole pairs have a greater chance of recombining within the bulksemiconductor body before they can migrate through it and combine at theanode and cathode to contribute to the cell's power output.Additionally, as in betavoltaics where the radioactive material isdeposited on the top surface of a semiconductor material only 50% of theparticles that are ejected by the radioactive material enter the siliconlayer to create electron-hole pairs. The other 50% of particles that areemitted away from the semiconductor material are wasted and onlygenerate heat.

By depositing the radioactive material in a very thin layer, somethingon the order of tens to hundreds of microns, the reabsorption can bereduced and almost eliminated since most of the emissions will be closeenough to the surface of the material to escape into the surroundingmaterials where they can be captured and used for power generation.Since the distance that a particle will travel through a solid materialdepends upon its energy as well as the material it is traveling through,the optimal thickness of the radioactive material layer will probably bedetermined based upon these factors. This thin layer approach is theoptimum structure for a radioactive material-based power cell. Whenstructured in this fashion, the goal is to maximize the emissions fromwithin the radioactive material will be able to escape the bulk materialand thereby limit the reabsorption effects. This is because theradioactive source material layer would be so thin that most of theemissions would have a high probability of escaping from the largesurface areas of the layer and only the relatively few emissions thatoccur along the axis of the layer would have a high probability ofrecombination. Reducing the thickness of the amorphous semiconductorlayers will allow some of the more energetic alpha and beta particles topass through the amorphous semiconductor layer and into the adjacentmaterial layers. This may not be a significant issue for the anode platebut could be for the bidirectional membrane material where bombardmentby high energy particles could result in premature failure. See FIG. 7.By placing layers of a semiconducting material 45 on one or both sidesof the radioactive material layer, the kinetic energy of the escapingalpha and beta particles can be used to generate electron-hole pairs inthe semiconducting material. An additional benefit to using an amorphoussemiconductor material in and around the radioactive material layer isthat radioactive materials that emit higher energy particles can be usedin the cell because the amorphous semiconducting material provides aprotective layer for the bidirectional membrane and anode materials byabsorbing much of the kinetic energy of these particles before theyreach the bidirectional membrane and anode. This opens up thepossibility of exploiting many more alpha and beta sources asradioactive materials for this battery which will lead to greater powercapacities. This process is described in greater detail below.

Referring to FIG. 10. When alpha or beta particles are spontaneouslyemitted from the radioactive source material, they will invariably runinto other atoms and release some of their kinetic energy to thoseatoms. Some percentage of these interactions result in an electron ofthe target atom being knocked free. The freeing of an electron 49 froman atom results in the atom having an overall positive charge. This isreferred to as a “hole” and is denoted as “h⁺” 50. The physicalinteraction of the alpha particle 47 and the beta particle 48 within thesemiconducting material can result in the formation of an electron-holepair 51. If the electron 49 is knocked free from the target atom so thatit cannot immediately recombine with the positive hole 50 then the twocharges have a chance to migrate across the cell to the anode 13 andcathode 19. If the electron is immediately recaptured by the target atomfrom which it was liberated, or another atom with a positive charge,then the two charges will cancel out and no useful energy can beobtained. This is known as recombination and results in this energybeing converted into heat. Since the amount of energy needed to free anelectron in the semiconducting material is much, much, lower than theenergy of the impinging alpha or beta particle, many electrons can beliberated and many holes formed within the semiconducting materialbefore the particle's kinetic energy is absorbed. This process creates acascade of electrons 49 and holes 50 from a single radioactive particle.FIGS. 7, 8 and 9 show variations of cell construction that can be usedto optimize the electron-hole generation and capture based upon variouscell chemistries and radioactive source particle energies. FIG. 10 showsthe electron-hole generation that occurs within a mixture of radioactivesource material and an amorphous semiconducting material. In thisapplication, shown in FIG. 9, the overall thickness of the mixture wouldnecessarily need to be much thicker than the very thin layer of the pureradioactive layer described earlier in order to increase the probabilitythat the particles will interact with many semiconductor material atomsto generate the greatest number of electron-hole pairs 51. The down sideto a thicker layer is the higher probability of recombination as theelectrons and holes migrate across this layer. Experimentation with theradioactive source material and the semiconducting material will need tobe done to optimize the layer 46 thickness. The optimal thickness of 46will, of course, depend upon the nature of the materials used.

Referring back to FIG. 7, with a thin layer of amorphous semiconductingmaterial 45, or any other material found to be a generous electron-holepair generator, on one or both sides of the radioactive material layer12, a single alpha or beta particle emission can be amplified hundredsor even thousands of times through interaction with the amorphoussemiconducting material as shown in FIG. 10. The resulting electrons 49and holes 50 will migrate across the semiconductor and radioactivematerial regions towards the appropriate cell plates. The longermigration path will increase the probability that the electrons andholes recombine before they reach the opposite plate.

The thickness of the semiconducting layers 45 will requireexperimentation to determine the optimal thickness. Two competingprocesses will tend cancel each other out. First, if the semiconductinglayer is too thin then too many of the alpha particles 23 and betaparticles 22 will pass through the layer without creating a cascade ofelectron-holes 51. Therefore, the thicker semiconductor layers 45 are,the greater the capture rate and the greater the electron-holegeneration. Competing with that process is the rate of recombinationwhich increases as the distance that the charges have to travel to reachthe anode and cathodes increases. Just as in a betavoltaic semiconductordirect conversion device, a too thick amorphous semiconductor materiallayer will allow too many of the electron-hole pairs to recombine withinthe material itself canceling out their electrical usefulness in thecell.

Another issue to consider in cell construction are the electricalcharacteristics of the radioactive source material. The electrons 49 orholes 50 may not be able to migrate across the radioactive materiallayer either because the radioactive material may itself be a naturalelectrical insulator which would inhibit charge migration or perhaps itmay have metal characteristics that promote the recombination of theelectrons 49 and holes 50 as they migrate from the semiconductingmaterial regions 45 across the radioactive source material region 12. Asolution to this problem, see FIG. 8, could be to place porous collectorplates 41 & 42 in or around the semiconducting material regions 45 andconnecting them together to provide a path for electrons to flow acrossthe radioactive material layer. The collector plates 41 & 42 inconjunction with connection 44 would provide a direct path for theelectrons to reach the cell anode 13 and would reduce the distance thatthey would have to travel through regions 12 & 45 which in turn wouldreduce the probability of recombination and eliminate the potentialelectrical characteristics issues of the radioactive source material. Inthis embodiment the collector plate 41 would allow the alpha particles47, and the holes 50 to pass through it to collect on the cathode plate19, while collecting the beta particles 48 the electrons 49 while alsoproviding a low impedance path through connection 43 to the anode 13.

See FIG. 9. Yet another embodiment would be to mix the amorphoussemiconductor material with the radioactive material, as describedabove, and applying the mixture in a thin layer 47 that would allow thealpha and beta particles along with the electron-hole pairs they createto migrate across this region without a great probability ofrecombination or reabsorption could be a very effective technique. Inthis case, the alpha and beta particles 47 & 48 respectively, along withthe electron-hole pairs 50 generated within the amorphous semiconductingmaterial would migrate to the appropriate plates under the influence ofthe cell's electric field, thus producing far greater output capacitythan the alpha and beta particles alone. One potential benefit to thisembodiment is that the semiconducting material could work to counteractthe electrical characteristics of the radioactive source material. Thesemiconducting material could act as a lower impedance path for theelectron and hole migration across this layer than what the radioactivesource material itself might have. This would aid the flow of chargesacross the radioactive layer. The net result would be a beneficialsemiconducting medium that produces cascades of electrons 49 and holes50 for each alpha particle 47 and beta particle 48. Again,experimentation to determine the optimum thickness of layer 46 and therelative amounts of the radioactive source material and semiconductingmaterial would be required. This layer's characteristics will also begreatly influenced by the materials used.

FIGS. 11 through 13 show the structure of the most basic radioactivedirect conversion cells using these teachings. It is anticipated thatthe techniques described herein can be exploited for radioactive directconversion devices where self-recharging of a secondary battery is notneeded or desired. Or where an external secondary battery or anotherenergy storage device may be connected to this basic cell for charging.FIG. 11 shows one of the simplest implementation employing the anode 13,cathode 19, PEM or bidirectional membrane 11 and a radioactive materiallayer 12. In this embodiment, a minimum external load would be requiredto keep the cell voltage from potentially achieving tens of thousands ofvolts. The cell voltage will be determined by the current generated andthe electrical resistance of the external load. Yet another embodimentof this cell can include the use of an anion exchange membrane either inconjunction with a PEM or bidirectional membrane layer or by itself asshown in FIG. 12. FIG. 12 shows the use of an anion exchange membrane 27that allows electrons and beta particles to flow from the radioactivematerial layer to the anode 13, with or without the use of the PEM orbidirectional exchange membrane 11, the characteristics of theradioactive material layer may provide sufficient electrical isolationto allow the elimination of the PEM or bidirectional membrane 11altogether. It is also anticipated that depending upon the electricalcharacteristics of the radioactive material layer, that this cell can befabricated without a PEM or bidirectional membrane layer 11 or an ionexchange membrane 27, as in FIG. 13. In this implementation, the anode,cathode and radioactive materials can be selected to produce a cellwherein an electric field is generated across the radioactive materiallayer sets the cell voltage and prevents short circuiting. Selecting ananode 13 material with electronegative tendency such as copper and ancathode 19 material with a electropositive tendency such as aluminum inconjunction with a semiconducting radioactive material or mixture couldresult in a cell that would not require any isolation membranes 11 and27. This option becomes more apparent when considering the use ofnonmetallic variations of radioactive materials, such as the oxides ofan elemental radioactive material or a mixture of a radioactive materialand a semiconducting material as described throughout thisspecification. Finally, a complementary chemical combination of radioisotope mixtures with perhaps an electrolyte layer between thisradioisotope material layer a the chemically complementary anode orcathode alloy material could develop an SEI (solid electrolyteinterface) layer could create an electrical bandgap sufficient for thiscell work without one or both of the isolation membranes.

All of the previous discussions pertaining to the basic self-rechargingcell discussed in previous sections of this specification apply to thesebasic cell implementations shown in FIGS. 11 through 13 minus thoseaspects specifically directed to the self-recharging and energy storagefeatures.

While the terms amorphous semiconductor and semiconductor are used todescribe a preferred embodiment of this technique, it is not to beinterpreted to be the only kind of material state that can be used togenerate the electron-hole pairs. In fact, any mater or materials thatproduce electron-hole pairs when bombarded with radioactive particleswhether amorphous, crystalline, polysilicon, nano-materials or any otherforms, can be a suitable potential source material for the presentinvention.

External Charging and Power Monitoring and Control

The inherent nature of this self-recharging battery does not precludethe capability of a fast charging in an external charging device. Anuclear battery of this design can be quickly charged by means ofinserting it into an external battery charger, similar to existingbattery charging devices using standard charging techniques.

A self-monitoring circuit to indicate to the user the level of chargethat the cell has at any given time can be incorporated into the device.Since the radioisotope would continuously charge the device, especiallywhen it is not in use, power cells using this technology can be swappedout of equipment, set aside, and they will recharge automatically.Alternatively, they could be charged more quickly by an external chargerdevice. The charge indicator would be powered by the device directly andwould let the user know how much power is available at any given time.

An electronic circuit that could control the internal and externalcharging and discharging characteristics of the battery could beincorporated as a safety/security aspect of the device. This circuitcould be used to control the total charge of the battery as well as todisable the battery recharge system to prevent automatic self-rechargingor external recharging. This functionality would be useful in abattlefield situation where the battery may be lost or stolen. In such asituation, the battery could be rendered useless, or at least preventedfrom recharging. Such a system can be implemented by incorporating abuilt-in electronic chip/circuit that would enable or disable rechargingor it could force discharging of the battery under specific conditionsthrough the resistive load material used to bleed off excess power. Forinstance, such a condition may be where a warfighter would carry a tinywireless control device (perhaps built into some other equipment) thatwould communicate with the battery controlling its functionality. Shouldthe battery become lost or stolen and unable to communicate with someapproved remote-control device, the battery could automatically renderitself useless, either by discharging or not allowing itself to berecharged externally or internally, thus rendering it useless to anyonebut those with the correct controller devices.

This same wireless control circuit could be used as a locator beaconthat could be activated under any number of predefined conditions suchas tampering or destruction of the cell in an attempt to obtain thenuclear materials.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to those skilled inthe art that various changes and modifications can be made thereinwithout departing from the spirit and scope thereof. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A battery comprising: a radioisotope material; acathode material connected to one side of the radioisotope material; ananode material connected to an opposite side of the radioisotopematerial; a housing capable of accommodating the radioisotope material,the anode material, and the cathode material; a first connection leadcoupled to the anode material; and a second connection lead coupled tothe cathode material.
 2. The battery of claim 1, further comprising anelectrolyte material positioned next to, around, or mixed with theradioisotope material.
 3. The battery of claim 1, further comprising asemiconducting material positioned next to, around, or mixed with theradioisotope material.
 4. A battery comprising: a radioisotope material;a first membrane having an electrolyte material, the first membraneconnected to one side of the radioisotope material; a cathode materialconnected to an opposite side of the first membrane and the electrolytematerial; an anode material connected to the other side of theradioisotope material; a housing capable of accommodating theradioisotope material, the first membrane, the electrolyte material, theanode material and the cathode material; a first connection lead coupledto the anode material; and a second connection lead coupled to thecathode material.
 5. The battery of claim 4, wherein the first membraneand the electrolyte material are each capable of passing positivelycharged particles and negatively charged particles between theradioisotope material and the cathode material.
 6. The battery of claim4, further comprising a semiconducting material positioned next to,around, or mixed with the radioisotope material.
 7. The battery of claim4, further comprising an electrochemical cell placed between the cathodematerial and the anode material.
 8. The battery of claim 4, wherein thefirst membrane and the electrolyte material are each composed as asolid-state structure.
 9. A battery comprising: a radioisotope materialhaving a first side and a second side; a first membrane having a firstelectrolyte material, a first side of the first membrane being connectedto the first side of the radioisotope material; a cathode materialattached to a second side of the first membrane and the firstelectrolyte material; a second membrane having a second electrolytematerial, a first side of the second membrane being connected to thesecond side of the radioisotope material; an anode material connected toa second side of the second membrane material and the second electrolytematerial; a housing capable of accommodating the radioisotope material,the first membrane, the second membrane, the first electrolyte material,the second electrolyte material, the anode material, and the cathodematerial; a first connection lead coupled to the anode material; and asecond connection lead coupled to the cathode material.
 10. The batteryof claim 9, wherein the first membrane and the first electrolytematerial are each capable of passing positively charged particles andnegatively charged particles between the radioisotope material and thecathode material.
 11. The battery of claim 9, wherein the secondmembrane and the second electrolyte material are each capable of passingpositively charged particles and negatively charged particles betweenthe radioisotope material and the anode material.
 12. The battery ofclaim 9, further comprising a semiconducting material positioned nextto, around, or mixed with the radioisotope material.
 13. The battery ofclaim 9, further comprising an electrochemical cell placed between tothe cathode material and the anode material.
 14. The battery of claim 9,wherein the first membrane and the first electrolyte material are eachcomposed as a solid-state structure.
 15. The battery of claim 9, whereinthe second membrane and the second electrolyte material are eachcomposed as a solid-state structure.
 16. A battery comprising: aradioisotope material having a first side and a second side, the firstside opposite to the second side; a first membrane connected to thefirst side of the radioisotope material; an anode material connected tothe first membrane; a cathode material connected to the second side ofthe radioisotope material; a housing capable of accommodating theradioisotope material, the first membrane and electrolyte material, theanode material and the cathode material; a first connection lead coupledto the anode material; and a second connection lead coupled to thecathode material.
 17. The battery of claim 16, wherein the firstmembrane is capable of passing positively charged particles andnegatively charged particles between the radioisotope material and theanode material.
 18. The battery of claim 16, further comprising asemiconducting material positioned next to, around, or mixed with theradioisotope material.
 19. The battery of claim 16, further comprisingan electrochemical cell placed between the cathode material and theanode material.
 20. The battery of claim 16, wherein the first membraneis composed as a solid-state structure.